This is a project by Carole Turley Voulgaris. The associated GitHub
repository is here. Feel free to
submit an issue with questions or comments.
Where do school children in Somerville live?
Here is map showing the approximate spatial distribution of
Somerville children enrolled in school (kindergarten through 8th grade)
based on data from the 2021 5-year sample of the American Community
Survey (see this technical
appendix for details). Each dot represents one student. Dots are
colored to differentiate between children in households with incomes
above the poverty level and those in households below the poverty
level.
This next map is similar, with each dot representing one student and
dot colors indicating whether the child is non-Hispanic and white or
either non-white or Hispanic.
Where is the middle of Somerville?
One way to think about the middle of a shape (for example, the
boundary of a city like Somerville) is its centroid. If you cut
out a piece of cardboard in the shape of Somerville, and you wanted to
balance your Somerville-shaped cardboard on the point of a pencil, the
centroid is where you’d need to put the pencil in order for it to
balance and stay level.
The population-weighted centroid is another useful way to
think about the middle of a geographic area. If you had that same piece
of cardboard, and you could stick a bunch of heavy pins to the top of
it, with each pin at a student’s home address, and then you
tried to balance it on the tip of a pencil, it would fall off your
pencil if you placed it at the centroid you were using before. The
population-weighted centroid is where you would have to put the pin to
balance your little Somerville cardboard now that it’s been weighted to
reflect the population of students. Another term for a
population-weighted centroid is the center of population.
When we’re thinking about where schools are needed, the center of the
student population is probably more relevant than the simple geometric
centroid, since land doesn’t go to school; children do.
Here is a map showing Somerville’s center of the K-8 student
population.
Average distances to school
Since Winter Hill Community Innovation School is so
centrally-located, it plays an important role in minimizing the average
distance between a Somerville student’s home and the nearest school.
Here is a map showing the walking distances to the nearest K-8
school
for K-8 students in Somerville.
Here is a map showing the same analysis under a hypothetical
condition where the Winter Hill building is removed from the set of
schools without being replaced.
Here is the same map for a hypothetical condition where the Winter
Hill building is replaced by a building at 8 Bonair Street.
Here is the same map for a hypothetical condition where the Winter
Hill building is replaced by a building at 554 Broadway.
Obviously, the students for whom the distance to the closest school
would change the most with the removal or relocation of WHCIS would be
those for who the location at 115 Sycamore Street would have otherwise
been the closest school (shown in the map below).
Here is a table showing the average walk time to the closest school
for K-8 students under each of the above scenarios. The first column
shows average walk times to the closest school for all students in
Somerville. The second column shows average walk times to the closest
school for those students for whom the school at 115 Sycamore Street is
currently the closest school.
| WHCIS at 115 Sycamore Street |
11.0 |
11.5 |
| WHCIS removed without replacement |
12.6 |
18.2 |
| WHCIS replaced with school at 8 Bonair Street |
12.1 |
17.9 |
| WHCIC replaced with a school at 554 Broadway |
12.3 |
17.2 |
